Optical device and method for manufacturing same

ABSTRACT

A method for manufacturing a structured optical device ( 1 ) starts with a substrate ( 2 ), on which is coated an alignment layer ( 3 ) and a liquid crystal polymer network layer ( 4 ). One of these layers can be created as a coating using a conventional technique. The other layer, either in a first step the alignment layer or in a second step the liquid crystal polymer network layer, is jet printed. The invention advantageously enables the making of a patterned liquid crystal polymer network which can be personalized upon manufacturing.

The invention relates to a method for manufacturing a liquid crystalpolymer network and an optical device manufactured according to themethod.

Such optical devices are usually based on birefringent layers formedfrom cross-linked Liquid Crystal Polymers (LCP). Generally, all kind ofLCP materials are possible, for instance apart from nematic materialsalso materials with different mesophases (such as cholesteric LCPs) orcontaining guest molecules (such as dichroic LCPs). For the alignment ofthe LCP prior and during the cross-linking, alignment layers are used. Awell-suited kind of alignment layers are photo-orientable LinearlyPhotopolymerisable Polymers (LPP). Backgrounds and manufacturing of suchLPP/LCP devices are disclosed in, for example, U.S. Pat. No. 5,389,698,U.S. Pat. No. 5,602,661, EP-A-0 689 084, EP-A-0 689 065, WO 98/52077, WO00/29878.

Conventional coating techniques such as spin-coating, slot-coating,meniscus-coating, bar-coating allow essentially a centralized massproduction of optical structured devices based on the LPP/LCPtechnology.

However, using these coating techniques it is not possible to provide apracticable method for the manufacturing of personalized opticalstructured devices, i.e. the production in small quantities or as singleitems with an each time varying pattern structure, especially if themanufacturing in addition should be decentralized. Moreover, with theseconventional coating techniques it is practically not possible to buildup stacks of layers with a pattern structure of different alignmentscombined with topographically variations of the layerthickness—especially not for microscopic dimensions in the ranges below300 micrometers.

A method according to the invention uses the characterizing features ofclaim 1 or claim 3. An optical device manufactured according to one ofthese methods is claimed in claim 17, and an optical security devicemanufactured according to one of these methods is claimed in claim 18.With the teaching of the invention it is advantageously possible tocreate single and personalized optical devices, especially securitydevices, in an easy to use and comparatively economical manner.

The method for manufacturing a structured optical device starts with asubstrate, which is, at least in certain areas, prepared as an alignmentlayer for liquid crystals, on which is coated, again at least in certainareas, a layer comprising a cross-linkable liquid crystal material. Oneof these layers can be created as a coating using a conventionaltechnique. The other layer, either in a first step the alignment layeror in a second step the layer comprising a cross-linkable liquid crystalmaterial, is jet printed in order to create a patterned liquid crystalpolymer network.

According to one preferred embodiment of the invention a patternedoptical device is manufactured based on mono-axial aligned layers suchas rubbed polyimide layers or mono-axially photo-oriented LPP layerswhich orient jet printed LCP layers according to the direction given bysaid alignment layers.

According to another embodiment of the invention a patterned opticaldevice is manufactured based one jet printed photo-oriented LPP layerswhich orient later applied LCP layers according to the direction givenby said alignment layers.

These optical devices can be applied, among others, in the fields ofdocument security, such as passports, identification cards (ID cards),driver licenses or special certificates, etc. against falsification oralteration; however, the invention is not limited to such field.

It is advantageous that these devices can be manufactured with a jetprinting technique. A jet printing technique can e.g. be based on piezojet printing or bubble jet printing. Especially; it is possible to use“ink-jet” printing techniques, largely used e.g. in today's computerprint-outputs.

These and other objects, features and advantages of the invention willbecome more apparent in light of the following detailed description ofembodiments thereof, as illustrated in the accompanying drawings, inwhich:

FIG. 1 is a schematic view of an LPP/LCP device made by jet-printing;

FIG. 2 is a schematic view of a reflective LPP/LCP device according toFIG. 1 with an appropriate inspection tool (polarizer) for viewing theinformation, here the character “P”;

FIGS. 3 a and 3 b are schematic views of a modified form of the deviceshown in FIG. 2; the device depicted in FIG. 3 is described in the firstembodiment;

FIGS. 4 a and 4 b are schematic views of the preferred device describedin the second embodiment;

FIGS. 5 a and 5 b are schematic views of the preferred device describedin the third embodiment;

FIGS. 6 a and 6 b are schematic views of the preferred device describedin the fourth embodiment;

FIG. 7 is a plan view of a more complex LPP/LCP device described in thefifth embodiment;

FIG. 8 is a plan view of a more complex LPP/LCP device including notonly LPP/LCP retarder layers but also a cholesteric filter and adichroic LCP layer; this device is described in the sixth embodiment;

FIG. 9 is a schematic drawing of the process flow of the decentralizedmanufacturing of personalized optical security LPP/LCP devices throughjet-printing;

FIG. 10 is a schematic drawing of the process of decentralizedmanufacturing of personalized optical security devices including an LCPlayer through jet-printing based on a optical security device describedin the fourth embodiment.

FIG. 1 is a schematic view of a structured LPP/LCP device 1 made byjet-printing. Such a device may for instance be used as a securitydevice. The process is started with a substrate 2 onto which analignment layer 3 is coated. The substrate 2 material can be for exampleplastic (e.g. polypropylene), the first alignment layer 3 may be an LPPlayer. The linearly photopolymerisable polymers (LPP) are initiallycontained in a solution 24 which is stocked in a first container 5 beingpart of a cartridges and printing unit 6 of an ink-jet printer. Examplesfor such ink-jet printers are disclosed in, for example, U.S. Pat. No.3,988,745, U.S. Pat. No. 4,385,304, U.S. Pat. No. 4,392,145, U.S. Pat.No. 3,747,120, U.S. Pat. No. 3,832,579, U.S. Pat. No. 3,683,212, U.S.Pat. No. 3,708,798, U.S. Pat. No. 4,660,058 and U.S. Pat. No. 5,754,198.

Line 10 shows schematically the droplets coating the substrate 2 andforming the alignment layer 3. After curing the first dried LPP layer 3,the same solution 24 is used to form a second alignment layer 13, inthis example shown in the form of the character “P” and having adifferent direction of orientation, e.g. with an different orientationindicated by the arrows 15 and 16.

Reference numeral 7 shows the control unit of the printer connected tothe first container 5 and to a second container 8. The second containeris filled with an LCP solution 9. Line 11 shows schematically thedroplets coating the alignment layer 3 and forming the LCP layer 4 and14.

Further explanations will be given with reference to FIG. 2 showingschematically an image 20 or 21 of such an LPP/LCP device made withjet-printing. Same references always depict same features in thedifferent Figures. Device 1 is a reflective LPP/LCP device according toFIG. 1 wherein the substrate 2 comprises a reflector (not explicitlyshown). References 25 or 26 indicate an appropriate inspection tool,here a polarizer, for viewing the information, here the character “P”.The polarizer 25 is orientated parallel to the orientation 15 of thealignment layer 3/LCP layer 4. The polarizer 26 is orientated parallelto the orientation 16 of the alignment layer 13/LCP layer 14. Therefore,polarizer 25 creates the image 20 of a dark “P” and polarizer 26 createsthe image 21 of a bright “P” surrounded with a dark zone.

The present invention describes a new technique of making LCP devices,which is based on jet printing. It advantageously allows thedecentralized manufacturing of personalized such devices in a reliableand cost-effective manner. A specific flow diagram illustrating thedecentralized manufacturing is depicted in FIG. 9. An example of acorresponding equipment is shown schematically in FIG. 10.

The personalization of optically structured security devices is anobjective which particularly the document security manufacturers andusers are asking for. Further, the combination of the decentralizedmanufacturing process together with the personalization of such opticalsecurity devices or other LCP and LPP/LCP devices not only openspossibilities in the field of document security but allows also to buildup a plethora of other applications using different optical effects. Thejet printing technique used may be ‘drop on demand’ methods or‘continues beam’ methods.

The process flow of FIG. 9 shows a possible way of making in adecentralized equipment personalized optically structured devices fore.g. document security, i.e. to protect e.g. passports, identificationcards, driver licenses or special certificates etc. againstfalsification or alteration. The personal data or other personalinformation as photographs are stored on a computer in a data base file100. The data is transferred to the manufacturing equipment 110. It ispossible and preferable to provide encoder means 102, encoding the datafrom the data base file 100, especially images or information forsecurity documents such as passports, ID documents and others, through asecurity software before passing the information to the manufacturingequipment 110 to ensure that the optical device can be perused only witha suitable decrypting tool.

Manufacturing equipment 110 comprises cartridges 112 as shown in FIG. 1,containing suitable coating materials, e.g. the materials mentioned inthe different embodiments in this description, and means 120 to performjet printing of materials, drying same and cross-linking LCP layers ifapplicable with light, especially isotropic UV light. The simplicity ofmeans 120 supports the possibility of decentralized production.

In a variation of the invention, it is possible to start with asubstrate, e.g. self-adhesive labels, already bearing an alignment layerthat was made in advance. In this case, the alignment layer may be ofany kind (rubbed polyimide or LPP or others), and the personalizedpattern structure is produced by suitably jet printing the LCP material.

Means 120 include printer means to operate the jet printer heads orcartridges which containing the LPP and LCP materials. Each singleprinter head will jet-print one specific material. In case of e.g. afour-head printer, four different materials may be jet-printed: e.g. thefirst head jet-prints a photo-orientable LPP material, the second headprints a LCP material, the third head prints a LCP material containingdichroic dyes, and the fourth head prints a cholesteric LCP material.Appropriate software will control the printing process.

The product 130 resulting from this method is a fully personalizedoptical security LCP device, ready to be applied. It can be used toproduce security products 132 as passports, ID documents and others.

FIG. 10 shows one example of an apparatus for manufacturing opticalstructured elements such as those described in embodiment 4. Theapparatus consists essentially of a jet-printing head 200 and anisotropic UV lamp 210. A computer 100 controls the printing process ontoe.g. sheets containing label substrates 2. The labels on the substrates2 were previously coated with an alignment layer 3 (e.g. photo-alignedLPP or rubbed polyimide). The jet-printed LCP layer 4 forms apersonalized pattern which—after a drying process through the heatedcylinder 220—is finally cross-linked by the isotropic UV light under aninert atmosphere (e.g. under a nitrogen atmosphere). The UV light isgenerated by the isotropic UV lamp 210 comprising a reflector 211. Thisleads to a solid-state plastic film. The labels which contain thepersonalized optical security device may then be transferred to e.g. apassport or to other documents.

FIG. 3 shows schematically the set-up of a first embodiment of anoptical device 1 according to the invention. FIG. 3 a shows the order ofthe layers wherein FIG. 3 b is an exploded view of FIG. 3 a. The firstLPP layer 3 is jet-printed on a substrate 2.

The substrate material can be for example plastic (e.g. polypropylene)or paper, preferably specially treated paper such that the paper surfaceis smooth and compatible with the LPP or LCP (including dichroic LCP andcholesteric LCP) solutions (e.g. paper coated with a polyethylenelayer). After the drying process the first alignment layer 3 is thenexposed to linear polarized UV light as described below (thepolarization direction 15 is say parallel to the long edge of thesubstrate 2 according to FIG. 3). Then, a second LPP layer 23 isjet-printed on top of the first LPP layer 3 having a different shapecompared to the first alignment layer 3. In FIG. 3 the second LPP layer23 has the shape of the character “P”. After the drying process thesecond alignment layer 23 is then exposed to linear polarized UV lightas described below (with a polarization direction 16 that is, forexample, 45 degrees to the long edge of the substrate 2 according toFIG. 3).

This procedure leads to an alignment area which shows two differentalignment capabilities: the area of first alignment layer 3 not coveredby second alignment layer 23 has an alignment capability along the longedge of the substrate (direction 15 in FIG. 3), and the area of secondalignment layer 23 (with the shape of “P”) has an alignment capabilityof 45 degrees to first alignment layer 3 (direction 16 in FIG. 3).

In the next step, a LCP material is jet-printed as a layer 4 onto bothalignment layers 3 and 23. When the solvent of the LCP materialevaporates from the LCP solution, the liquid crystal molecules alignaccording to the alignment information of the two LPP layers 3 and 23. Across-linkage as described below forms then a solid state plastic film.This terminates the manufacturing process of the optical structuredLPP/LCP device 1.

The information (here the character “P”) can be visualized with one ortwo linear polarizer(s), one polarizer for reflective devices, twopolarizers for transmissive devices. By rotating the polarizer or thedevice 1, the image changes from positive to negative.

FIG. 4 shows schematically the set-up of a second embodiment of a device31 according to the invention. FIG. 4 a shows the order of the layerswherein FIG. 4 b is an exploded view of FIG. 4 a. The substrate 2 isalready coated with a previously manufactured first alignment layer 33having an alignment direction 15 along the long edge of the substrate inFIG. 4. The substrate 2 material can be chosen as in the firstembodiment. It is possible that the first alignment layer 33 covers adefinite area as shown in FIG. 4 or the first alignment layer 33 coversthe whole substrate 2.

A second LPP layer 23 is jet-printed on top of the first alignment layer33 having a different shape compared to the latter layer. In FIG. 4 thesecond LPP layer 23 has the shape of the character “P”. After a dryingprocess, the second layer 23 is then exposed to linear polarized UVlight as described below (the polarization direction 16 is say 45degrees to the long edge of the substrate 2 according to FIG. 4). Thisprocedure leads to a an alignment area which shows—as in the case of thefirst embodiment—two different alignment capabilities: the arearesulting, from the first alignment layer 33 not covered by the secondalignment layer 23 has an alignment capability along the long edge ofthe substrate 2 (FIG. 4), and the second LPP layer 23 (having the shapeof “P”) has an alignment capability 45 degrees to first alignment layer33.

In the next step the LCP material is jet-printed as a layer 4 onto firstalignment layer 33 and second LPP layer 23. When the solvent isevaporated from the LCP solution, the liquid crystal molecules 4 alignaccording to the alignment information 15 and 16 of the two LPP layers33 and 23, respectively. A cross-linkage as described below forms then asolid state plastic film. This terminates the manufacturing process ofthe optical structured LPP/LCP device 31. The information (here thecharacter “P”) can be visualized with one or two linear polarizer(s),one polarizer for reflective devices, two polarizers for transmissivedevices. By rotating the polarizer or the device the image changes frompositive to negative.

FIG. 5 shows schematically the set-up of a third embodiment of a device41 according to the invention. FIG. 5 a shows the order of the layerswherein FIG. 5 b is an exploded view of FIG. 5 a. A single LPP layer 23is jet-printed on a substrate 2 and forms a pattern such as a picture, agraphic, or one or several alpha-numeric characters. In FIG. 5 thejet-printed LPP area forms e.g. the character “P”. The substratematerial can be chosen as in the first embodiment. After the dryingprocess, the substrate including the LPP area 23 is then exposed tolinear polarized UV light as described below (the polarization direction16 is say 45° to the long edge of the substrate 2 according to FIG. 5).This procedure leads to a an area which shows two different alignmentcharacteristics the section resulting from the jet-printed. LPP area 23(LPP layer 23 described in the third embodiment has the shape of “P”)has an alignment capability of 45° to the long edge of the substrate(FIG. 5), the remaining area has no alignment information.

In the next step, the LCP material is jet-printed as a layer 4 onto thealignment layer 23 and also onto the remaining area of the substrate 2according to FIG. 5. This specific area forms the LCP layer 4 shown inFIG. 5. When the solvent is evaporated from the LCP solution, the liquidcrystal molecules on top of the LPP layer 23 align according to thealignment information 16 of the LPP layer 23. The remaining LCP areashows isotropic alignment. A cross-linkage as described below forms thena solid state plastic film. This terminates the manufacturing process ofthe optical structured LPP/LCP device 41. The information. (thecharacter “P”) can be visualized with one or two linear polarizer(s),one polarizer for reflective devices, two polarizers for transmissivedevices. By rotating the device, the image changes—depending on theorientation of the polarizer—from positive to invisible or from negativeto invisible depending on the acting mode which can be reflective ortransmissible.

FIG. 6 shows schematically the set-up of a fourth embodiment of a device51 according to the invention. FIG. 6 a shows the order of the layersand FIG. 6 b is an exploded view of FIG. 6 a. In a first step analignment layer 33 was applied to the substrate 2. The alignment layermay consist of a photo-orientable material such as an LPP material or ofanother alignment material such as rubbed polyimide or any other film orsurface which is able to align % liquid crystal molecules. The solealignment layer 33 may be mono-axial as indicated in FIG. 6, but designswith more than one aligning direction are also possible. The substratematerial can be chosen as in the first embodiment. The manufacturing ofthe alignment layer 33 can be done in advance and in a different place,that is, the substrates 2 including the alignment layer 33 may bepre-manufactured.

Then an LCP solution is jet-printed as a layer 54 onto that alignmentlayer 33 and forms a kind of information such as a picture, a graphicalpattern, or one or several alpha-numeric characters. In FIG. 6 the shapeof the jet-printed LCP area 54 forms the character “P”. When the solventis evaporated from the LCP solution, the liquid crystal molecules on topof the alignment layer 33 align according to the alignment information15 of said alignment layer 33. On the remaining alignment area no LCP ispresent. A cross-linkage as described below forms then a solid stateplastic film. This terminates the manufacturing process of the opticalstructured device 51. The information (here the character “P”) can bevisualized with one or two linear polarizer(s), one polarizer forreflective devices, two polarizers for transmissive devices. By rotatingthe device the image changes—depending on the orientation of thepolarizer—from positive to invisible or from negative to invisibledepending on the acting mode.

FIG. 7 shows schematically the set-up of a fifth embodiment of a device61 according to the invention which consists of a topographicallycomplex orientation pattern including one (66) or several (67) LPP/LCPlayers. In a fist step, a first LPP layer 3 is jet-printed on a certainarea 68 of a substrate 2. The substrate material can be chosen as in thefirst embodiment.

After the drying process, the first layer 3 is then exposed to linearpolarized UV light as described below (the polarization direction 17 isfor instance perpendicular to the long edge of the substrate 2). Then, asecond LPP layer 43 is jet-printed on an area 69 of the substrate 2different from the area 68 of the first alignment layer 3. The secondLPP layer 43 may have a different shape compared to the first LPP layer3. After the drying process, the second LPP layer 43 is then exposed tolinear polarized UV light as described below (the polarization direction15 is for instance parallel to the long edge of the substrate 2).

Then, these two LPP layers 3 and 43 are jet-printed with LCP materialsuch that different thickness d₂ and d₁ of the LCP layers 4 and 44result. When the solvent is evaporated from the LCP solution, the liquidcrystal molecules align according to the alignment information of thetwo LPP layers 3 and 43. A cross-linkage as described below then forms asolid state plastic film.

As shown in FIG. 7, on top of the LCP area 44 a further LPP layer isjet-printed to form the third LPP area 53. After the drying process, thethird LPP layer 53 is then exposed to linear polarized UV light asdescribed below (the polarization direction 17 is say perpendicular tothe long edge of the substrate 2). Then, a further LPP layer 63 isjet-printed onto the LCP layer 4. The further LPP layer 63 may have adifferent shape compared to the LPP layers 3, 43 and 53. After thedrying process, the further LPP layer 63 is then exposed to linearpolarized UV light as described below (the polarization direction 18 issay 135 degrees to the long edge of the substrate 2). Then these two LPPlayers 53 and 63, not contacting the substrate 2, are jet-printed withLCP material such that different thickness d₃ and d₄ of the LCP layers64 and 74 result. When the solvent is evaporated from the LCP solution,the liquid crystal molecules align according to the alignmentinformation of the two LPP layers 53 and 63 or—if no LPP layer ispresent as in area 67—according the adjacent LCP layer 44 below. In FIG.7, this happens with the left part of the LCP area 64. Normally, the LPPlayer thickness (around 50 nm) is much smaller than the thickness of theoptically active LCP layer. Thus, in FIG. 7 the thickness d₃ of the LCPlayer 64 is depicted only with one thickness instead of correctly two.On the right side of area 68 there is no second LPP/LCP layer andtherefore this area 66 consists of only one LPP/LCP layer. Across-linkage as described below forms, then a solid state plastic film.This terminates the manufacturing process of the optical structuredLPP/LCP device 61. The information can be visualized with one or twolinear polarizer(s), one polarizer for reflective devices, twopolarizers for transmissive devices.

The optical devices 61 manufactured as shown in FIG. 7 and describedabove may show very complex color patterns. By rotating the polarizer orthe device the image changes from positive to negative or from one colorpattern to its complementary color counterpart. The process described inthis embodiment allows the manufacturing of complex optical devices suchas e.g. sophisticated optical structured security elements or specificinterference color filters.

FIG. 8 shows schematically the set-up of a sixth embodiment whichconsists of a topographically complex orientation pattern including one(76) or more (77) LPP/LCP layers combined with dichroic and/orcholesteric liquid crystal layers. In a first step, a first LPP layer 3is jet-printed on a substrate 2. The substrate material can be chosen asin the first embodiment. In case of cholesteric layers, a lightabsorbing dark background leads to better reflective properties for onemode of circularly polarized light, whereas the other mode issubstantially absorbed. After the drying process, the first layer 3 isexposed to linear polarized UV light as described below (thepolarization direction 18 is say 135 degrees to the long edge of thesubstrate 2). Then, a second LPP layer 43 is jet-printed beside thefirst alignment layer 3. The second LPP layer 43 may have a differentshape compared to the first LPP layer 3. After the drying process, thesecond LPP layer 43 is then exposed to linear polarized UV light asdescribed below (the polarization direction 15 is say parallel to thelong edge of the substrate 2). Then, these two LPP layers 3 and 43 arejet-printed with LCP material such that different thicknesses d₁ and d₂of the LCP layers 84 and 4 result. According to FIG. 8, the LCP layer 84is a dichroic layer, which means that the LCP layer 84 contains dichroicdyes as described below. The dichroic dyes may be cross-linkable. Whenthe solvent is evaporated from the LCP solution, the liquid crystalmolecules align according to the alignment information of the two LPPlayers 3 and 43. A cross-linkage as described below forms then a solidstate plastic film.

As shown in FIG. 8, on top of the LCP area 84 further LPP material isjet-printed to form the LPP area 53. After the drying process, the LPPlayer 53 is exposed to linear polarized UV light as described below (thepolarization direction 17 is say perpendicular to the long edge of thesubstrate 2). Then, the LPP layer 53 and part of the LCP layers 4 and 84are jet-printed with LCP material such that different thicknesses d₃ andd₄ of LCP layers 64 and 74 result. According to FIG. 8, the LCP layer 74consists of a cholesteric liquid crystal layer with a specific pitch.The manufacturing process of such a cholesteric layer is describedbelow. When the solvent is evaporated from the LCP solutions, the liquidcrystal molecules align according to the alignment information of theLPP layer 53 or—if no LPP layer is present as on LCP layer 4 and on LCPlayer 84 in ar a 77—according to the adjacent LCP layer 84 below.Normally, the LPP layer thickness (around 50 nm) is much smaller thanthe thickness of the optically active LCP layer. Thus, in FIG. 8 thethickness d₃, of the LCP layer 64 is depicted only with one thicknessinstead of correctly two. A cross-linkage as described below forms thena solid state plastic film. Then, a further LPP layer 63 is jet-printedonto the cholesteric LCP layer 74 and, after drying, exposed to linearpolarized UV light (with the polarization direction 17 perpendicular tothe long edge of the substrate 2). The LPP layer 63 is then jet-printedwith LCP material to form an LCP layer 94. A cross-linkage as describedbelow then forms a solid state plastic film. This terminates themanufacturing process of the optical structured LPP/LCP device 71.

The complex information can be visualized with one or two linearpolarizer(s), one polarizer for reflective devices, two polarizers fortransmissive devices. The optical devices 71 described in thisembodiment may show very complex color patterns. By rotating thepolarizer or the device the image changes from positive to negative orfrom one color pattern to its complementary color counterpart. Theprocess described in this embodiment again shows the possibility ofmanufacturing complex and sophisticated optical devices.

For the production of the LPP layers, suitable LPP materials are knownto a person skilled in the art. Examples are for instance described inpatent publications EP-A-0 611 786, WO-96/10049 and EP-A-0 763 552. Theyinclude cinnamic acid derivatives and ferulic acid derivatives. For theexamples described above, the following LPP material

was used as a 10 percent solution in a solvent mixture of MEK(methyl-ethyl ketone) and ethyl acetate (ratio MEK:ethyl acetate=1:1).The viscosity was between 2 and 4 mPas. Depending on the type of ink-jetprinting head used also higher viscosity up to about 80 cP are possible.The layers were exposed to linearly polarized light from a mercuryhigh-pressure lamp for 10 to 550 seconds (depending on the strength ofthe lamp and on the characteristics of LPP and LCP layers) at roomtemperature.

For the production of the LCP layers in the examples the followingcross-linkable liquid crystal diacrylate components

were used in a supercoolable nematic mixture (Mon1 80%, Mon2 15%, Mon35%) having a particularly low melting point (Tm˜35° C.) thus making itpossible to prepare the LCP layer at room temperature. The mixture wasdissolved in MEK. If required, well-known additives may also be present,such as e.g. phenol derivatives for stabilisation or photoinitiatorslike Irgacure®. By means of varying the concentration, it was possibleto adjust the LCP layer thickness over a wide range leading to differentoptical retardations (e.g. about λ/4 to λ/2 for almost black and whitedevices for reflective mode or transmissive mode respectively) of theLCP retarder layers. For cross-linking the liquid crystal monomers, thelayers were exposed to isotropic light from a xenon lamp in an inertatmosphere.

For the production of the dichroic LCP layers, the nematic mixture ofcross-linkable liquid crystal diacrylate components as described abovewas used, additionally containing one or more dichroic dyes. As dichroicdyes, the mixture contained for instance a blue antraquinone dye B3 anda red azo dye R4 (structures see below) in concentration 2 weight % and1 weight % respectively.

By means of varying the concentration in a solvent such as MEK, it waspossible to adjust the LCP layer thickness over a wide range leading todifferent extinction values of the dichroic polarizer.

For the production of the cholesteric LCP layers, a procedure similar tothat of the nematic LCP layer was used. However, the nematic mixture wasadditionally doped with cholesteric material inducing a pitch. Asuitable chiral dopant was e.g. ST31L which shows a left-handed helicalsense.

The concentration of the chiral dopant was 4% to 9%, more preferable 5%to 6%. This induces the desired reflective wavelength band in thevisible range, but by changing the concentration also reflectivewavelength bands in the UV or IR range can be realized. By means ofvarying the concentration in a solvent such as MEK, it was possible toadjust the cholesteric LCP layer thickness over a wide range leading todifferent reflection properties. The thickness of the cholesteric layerwas 1 to 10 micrometers, depending on the wavelength range intended.

The optical effects described above, as well as the corresponding layerstructures and material compositions, represent only some of manypossibilities according to the invention. They may in particular becombined in a wide variety of ways, which will be especiallyadvantageous for the development and application of authenticatingelements. Of course, any other kind of birefringent layer than the LCPlayer described may also be used to produce an optical effect that canbe employed in optical devices.

It is furthermore possible for the examples described above, to use notan LPP alignment layer but a different alignment layer which, accordingto the desired optical property and resolution, has the same or similarproperties to an LPP layer. It is also conceivable to produce theorientation required for a retarder layer using a correspondinglystructured substrate. A structured substrate of this type can, forexample, be produced by embossing, etching and scratching.

1-18. (canceled)
 19. A method for manufacturing a liquid crystal polymer network having a pattern structure, comprising: providing a substrate; jet printing a first alignment layer, which comprises a material to which an aligning property can be imparted by exposure to polarized light, in a first pattern onto the substrate; exposing the first alignment layer to a first polarized light; coating the substrate bearing the alignment layer with a first layer comprising a cross-linkable liquid crystal material; allowing the liquid crystal material to align; and cross-linking the liquid crystal material.
 20. A method according to claim 19, further comprising: jet printing a second alignment layer, which comprises a material to which an aligning property can be imparted by exposure to polarized light, in a second pattern on or adjacent to the first alignment layer; and exposing the second alignment layer to a second polarized light having a polarization different from the first polarized light.
 21. A method according to claim 19, wherein the first alignment layer covers a first area creating an image element and wherein the first layer comprising a cross-linkable liquid crystal material covers a second area including at least said image element.
 22. A method according to claim 20, further comprising: jet printing at least one further alignment layer in at least one further pattern adjacent the first and the second alignment layers; and exposing the at least one further alignment layer to a further polarized light.
 23. A method according claim 22, wherein data representing the first, second, and further patterns are stored in a memory of a computer system and wherein the computer system controls jet printing of the alignment layer and wherein the computer system further controls coating of the cross-linkable liquid crystal onto the substrate.
 24. A method according to claim 22, wherein at least one of the first, second, and further alignment layers comprises a layer containing a linearly photopolymerisable material.
 25. A method according to claim 22, wherein the first, second, and further polarized lights to which the first, second, and further alignment layers are exposed is selected from one of linearly and elliptically polarized.
 26. A method according to claim 19, wherein the jet printing is selected from one of a piezo jet printing method and a bubble jet printing method.
 27. An optical device comprising a liquid crystal polymer network having a pattern structure manufactured according to claim
 19. 28. An optical device according to claim 27, which is an optical security device.
 29. A method for manufacturing a liquid crystal polymer network having a pattern structure, comprising: providing a substrate comprising a first alignment layer; jet printing a first layer comprising a cross-linkable liquid crystal material in a first pattern; allowing the liquid crystal material to align; and cross-linking the liquid crystal material.
 30. A method according to claim 29, wherein the first alignment layer comprises at least a second pattern.
 31. A method according to claim 29, further comprising: producing the first alignment layer by one of embossing, etching, and scratching.
 32. A method according to claim 29, further comprising: jet printing a second alignment layer, which comprises a material to which an aligning property can be imparted by exposure to polarized light, in a second pattern on or adjacent to the first alignment layer; and exposing the second alignment layer to a polarized light such that the second alignment layer is oriented in a direction different to the orientation of the first alignment layer.
 33. A method according to claim 29, wherein at least two additional layers comprising a cross-linkable liquid crystal material are jet printed adjacent to each other.
 34. A method according to claim 29, further comprising: jet printing at least one further alignment layer, which comprise a material to which an aligning property can be imparted by exposure to polarized light, on at least one of the already existing layers comprising a cross-linkable liquid crystal material; exposing the at least one further alignment layer to polarized light; jet printing at least one further layer comprising a cross-linkable liquid crystal material; and cross-linking the at least one further layer comprising a cross-linkable liquid crystal material.
 35. A method according to claim 29, wherein the first alignment layer covers an area creating an image element and wherein the first layer comprising a cross-linkable liquid crystal material covers a second area encompassing at least said image element.
 36. A method according to claim 29, wherein the first layer comprising a cross-linkable liquid crystal material covers an area creating an image element on the first alignment layer covering a bigger area encompassing at least said image element.
 37. A method according to claim 30, wherein data representing the first and at least second patterns are stored in a memory of a computer system and wherein the computer system controls the jet printing of the cross-linkable liquid crystal material.
 38. A method according to claim 32, wherein at least one alignment layer comprises a layer containing a linearly photopolymerisable material.
 39. A method according to claim 32, wherein the first and the second polarized light are selected from one of linearly and elliptically polarized light.
 40. A method according to claim 29, wherein at least one layer comprising a cross-linkable liquid crystal material further comprises at least one dichroic dye.
 41. A method according to claim 29, wherein the jet printing is selected from a piezo jet printing method and a bubble jet printing method.
 42. An optical device comprising a liquid crystal polymer network having a pattern structure manufactured according to claim
 29. 43. An optical device according to claim 42, which is an optical security device.
 44. A method according to claim 19, wherein at least one layer comprising a cross-linkable liquid crystal material further comprises at least one dichroic dye. 